KR20080111315A - Liquid crystal display and driving method thereof - Google Patents

Abstract

A liquid crystal display device and a driving method thereof are provided to improve display quality by supplying a data stretched gamma curve to a moving picture. m x n liquid crystal cells are arranged in a liquid crystal display device in a matrix type. In a liquid crystal display panel(33), a TFT is formed in a cross region by crossing the m data lines and n gate lines. A data driving circuit(35) supplies a data signal to the data lines of the LCD panel. A gate driving circuit(34) supplies a scan signal to gate lines. A moving picture detection unit(38) is built in a timing controller(36). A gamma value according to input data is mapped in a look up table(39). A timing controller generates a signal for controlling data driving circuit and the gate driving circuit.

Description

Liquid Crystal Display and Driving Method Thereof

1 is a block diagram schematically showing a driving device of a liquid crystal display device;

2 is an image captured by activating a video window under a computer operating system (Windows).

3 is a block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

4 to 6 are diagrams illustrating a detection process of a video region according to an embodiment of the present invention.

7 is a screen showing a black area in a moving picture area.

8 is a diagram illustrating a border search in a video area.

9 is a screen showing a video according to the change of the slope of the gamma curve.

10 is a screen illustrating a video according to an average gamma curve

11 to 13 are screens and graphs showing a video according to the stretched gamma curve.

14 to 15 are flowcharts showing a driving procedure of the liquid crystal display according to the embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

LCD panel: 3, 33, 40 Gate driving circuit: 4, 34

Data driver circuit: 5, 35 Timing controller: 6, 36

System: 7,37 video detection unit: 38

Lookup table: 39 Still image area: 50

Video area: 40

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly, to improve the display quality of a moving image displayed on a screen such as a still image.

 The liquid crystal display displays an image by adjusting light transmittance of liquid crystal cells according to a video signal. The liquid crystal display device is implemented in an active matrix type in which switching elements are formed in each cell, and thus are used in display devices such as computer monitors, office equipment, and cellular phones. As a switching element used in an active matrix type liquid crystal display device, a thin film transistor (hereinafter referred to as TFT) is mainly used.

1 schematically shows a driving device of a conventional liquid crystal display.

Referring to FIG. 1, in a driving apparatus of a conventional liquid crystal display, m × n liquid crystal cells Clc are arranged in a matrix type, m data lines D1 to Dm and n gate lines G1 to When Gn is crossed, a liquid crystal display panel 3 having a TFT formed at the intersection thereof, a data driving circuit 5 for supplying a data signal to the data lines D1 to Dm of the liquid crystal display panel 3; The data driving circuit 5 and the gate driving circuit 4 are controlled by using the gate driving circuit 4 for supplying the scan signal to the gate lines G1 to Gn and the synchronization signal supplied from the system 7. The timing controller 6 is provided.

The system 7 supplies the vertical / horizontal synchronization signals Vsync and Hsync, the clock signal DCLK, the data enable DE and the data R, G and B to the timing controller 6.

The liquid crystal display panel 3 includes a plurality of liquid crystal cells Clc disposed in a matrix at the intersections of the data lines D1 to Dm and the gate lines G1 to Gn. The liquid crystal cell Clc is connected to a drain electrode of a thin film transistor (“TFT”), and a source electrode is connected to gate lines G1 to Gn. In the liquid crystal cell Clc, the liquid crystal is driven by the electric field difference between the opposite common electrode Vcom. The TFT supplies the data signal supplied from the data lines D1 to Dm to the liquid crystal cell Clc in response to the scan signal supplied from the gate lines G1 to Gn. In addition, a storage capacitor Cst is formed in each of the liquid crystal cells Clc. The storage capacitor Cst is formed between the pixel electrode of the liquid crystal cell Clc and the front gate line, or is formed between the pixel electrode of the liquid crystal cell Clc and the common electrode line to maintain a constant voltage of the liquid crystal cell Clc. Let's do it.

The data driving circuit 5 converts the digital video data R, G, and B into analog gamma voltages corresponding to the gray scale values in response to the control signal DDC from the timing controller 6, and converts the analog gamma voltages. Supply to the data lines D1 to Dm.

The gate driving circuit 4 supplies scan pulses sequentially to the gate lines G1 to Gn in response to the control signal GDC from the timing controller 6 to supply the data voltage. Select the horizontal line.

The timing controller 6 controls to control the gate driving circuit 4 and the data driving circuit 5 by using the vertical / horizontal synchronization signals Vsync and Hsync and the clock signal DCLK input from the system 7. Generate signals DDC and GDC.

In such a liquid crystal panel, when a computer operating system such as FIG. 2 activates a video in a small window in a window of Microsoft Corporation, conventionally, the same gamma voltage is applied to a still image region or a video region without distinguishing between the video region and the still image region. Since the image quality of the moving picture area activated in a small window is not significantly different from that of the still picture area, it is difficult to express more dynamic and dynamic video.

Accordingly, the present invention has been made to solve the problems occurring in the related art, and an object of the present invention is to provide a liquid crystal display device and a driving method thereof to increase the display quality of a moving image displayed on a screen such as a still image.

In order to solve the above object, a liquid crystal display according to an embodiment of the present invention comprises a moving picture detection unit for determining the moving picture data and still image data by comparing the brightness of the input data and partitions the moving picture area to display the moving picture data; A gamma correction unit for converting gamma characteristics of the moving image data to be displayed in the moving image region from those of the still image data; And a display driving circuit which displays data on which the gamma characteristic is converted by the gamma correction unit on the liquid crystal display panel.

The background screen on which the video area and the still image data are displayed is displayed together on one screen.

The moving picture detector detects the luminance of the input data during a plurality of frame periods and compares the luminance in units of pixels, and the data in which the pixel luminance values of the previous frame period and the next frame period are greater than or equal to a predetermined reference value during the plurality of frame periods. It is characterized by determining that the video data.

In accordance with another aspect of the present invention, there is provided a method of driving a liquid crystal display, comprising: determining moving image data and still image data by comparing luminance of input data; Partitioning a video region in which the video data is to be displayed; Converting a gamma characteristic of the moving image data to be displayed in the moving image region from a gamma characteristic of the still image data; And displaying the converted data of the gamma characteristic on a liquid crystal display panel.

The background screen on which the video area and the still image data are displayed is displayed together on one screen.

The determining of the moving image data and the still image data may include detecting a luminance of input data for a plurality of frame periods and comparing the luminance for each pixel unit; And determining, as moving image data, data whose pixel luminance values of the previous frame period and the next frame period are equal to or greater than a predetermined reference value during the plurality of frame periods.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 3 to 15.

3 is a block diagram of a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 3, in the liquid crystal display according to the exemplary embodiment of the present invention, m × n liquid crystal cells Clc are arranged in a matrix type, m data lines D1 to Dm and n gate lines ( When G1 to Gn cross, a liquid crystal display panel 33 having a TFT formed at the intersection thereof and a data driving circuit 35 for supplying a data signal to the data lines D1 to Dm of the liquid crystal display panel 33. And a lookup table in which a gate driving circuit 34 for supplying a scan signal to the gate lines G1 to Gn, a video detector 38 embedded in the timing controller 36, and a gamma value corresponding to input data are mapped. And a timing controller 36 for generating a signal for controlling the data driving circuit 35 and the gate driving circuit 34.

The system 37 supplies timing signals 'Vsync1', 'Hsync1', 'DCLK1', and 'DE1' to the timing controller 36. The timing signal is a data enable signal indicating a period in which the vertical / horizontal sync signals Vsync1 and Hsync1, the dot clock DCLK1 for sampling digital video data, and the digital video data R, G, and B exist. DE1). 'Vsync2', 'Hsync2', 'DCLK2', and 'DE2' are timing signals modulated by the timing controller 36. 'Ri', 'Gi', and 'Bi' are three primary color digital video data supplied from the system 37 to the timing controller 36, and 'R _O ', 'G _O ', and 'B _O ' are timing controllers. It is three primary color digital video data supplied to the data driving circuit 35 as data modulated by the moving picture detecting unit 38 in 36.

 In the liquid crystal display panel 33, liquid crystal is injected between two glass substrates. The data lines D1 to Dm and the gate lines G1 to Gn formed on the lower glass substrate of the liquid crystal display panel 33 are perpendicular to each other. Thin film transistors (hereinafter referred to as TFTs) formed at the intersections of the data lines D1 to Dm and the gate lines G1 to Gn are applied to the scan signals from the gate lines G1 to Gn. In response, data voltages from the data lines G1 to Gn are supplied to the liquid crystal cell Clc. For this purpose, the gate electrode of the TFT is connected to the corresponding gate lines G1 to Gn, the source electrode is connected to the data lines D1 to Dm, and the drain electrode of the TFT is a pixel electrode of the liquid crystal cell Clc. A black matrix, a color filter, and a common electrode are formed on the upper glass substrate of the liquid crystal display panel 33. The light exit surface of the upper glass substrate and the light incident surface of the lower glass substrate of the liquid crystal display panel 33 are formed. Polarizing plates having orthogonal optical axes are attached to each other, and an alignment film for setting the pretilt angle of the liquid crystal is formed on each of the liquid crystal facing surface of the lower glass substrate and the liquid crystal facing surface of the upper glass substrate. Each of the liquid crystal cells Clc is formed with a storage capacitor Cst, which is formed between the pixel electrode of the liquid crystal cell Clc and the front gate line, or is disposed between the pixel electrode of the liquid crystal cell Clc and the pixel electrode. Is formed between the electrode lines (Vcom) serves to maintain a constant voltage of liquid crystal cells (Clc).

The data driving circuit 35 converts the digital video data R _O , G _O , B _O into an analog gamma compensation voltage corresponding to the gray scale value in response to the control signal DDC from the timing controller 36. The analog gamma compensation voltage is supplied to the data lines D1 to Dm of the liquid crystal display panel 33 as a data voltage.

The gate driving circuit 34 generates scan pulses of the gate voltages VGH and VGL in response to the control signal GDC from the timing controller 36, and sequentially scans the scan pulses to the gate lines G1 to Gn. The horizontal line of the liquid crystal display panel 33 to which the data signal is supplied is selected.

The video detecting unit 38 receives digital video data Ri, Gi, and Bi input from the system 37. The moving picture detecting unit 38 converts the digital video data Ri, Gi, and Bi into modulation data YUV, and detects the moving picture area by comparing the luminance Y of each pixel in units of frames. For example, let's compare the luminance component of each pixel between two frames. The moving image detector 38 stores the modulated data YUV, which converts the digital video data Ri, Gi, Bi, input data of the previous frame, into the luminance component Y and the chrominance component U, V, and stores the current frame. The digital video data Ri, Gi, and Bi are modulated data YUV converted into luminance components Y and chrominance components U and V are also stored to compare luminance components of each pixel between two frames. . That is, the moving picture area is determined as the moving picture area when the difference between the luminance component of each pixel of the previous frame and each pixel of the current frame is equal to or greater than 40 which is the threshold (reference value). Will be determined. The moving picture area is accurately determined by the moving picture detecting unit 38 during a plurality of frame periods, particularly during the 60 frame period.

4 to 6 illustrate a process of determining a video region during a 60 frame period according to an embodiment of the present invention.

As shown in FIGS. 4 to 5, the video detector 38 sequentially compares the luminance components of the modulation data YUV supplied to each pixel of the liquid crystal display panel every 60 frames. That is, during the period of one frame, the video detecting unit 38 modulates the modulation data supplied to the pixels of the last data line and the last gate line, starting with the modulation data values supplied to the pixels of the first data line and the first gate line of the liquid crystal display panel. Retrieve and store data values. In addition, during the two-frame period, the video detector 38 performs modulation data supplied to the pixels of the last data line and the last gate line, starting with the modulation data values supplied to the pixels of the first data line and the first gate line of the liquid crystal display panel. Retrieve and store the value. The modulation data value of each pixel searched and stored during this one frame period and the modulation data value of each pixel searched and stored during the two frame periods are compared with each other, and each pixel value counts the number of conversions. That is, if the difference between the luminance components, which is the modulation data of each pixel, is 40 or more during the period of two frames, the number of conversions 1 is counted for the pixel. In this manner, the video detecting unit 38 compares the luminance component, which is the modulation data of each pixel, every frame for 60 frames, and counts the number of conversions through the comparison. When the number of conversions counted for each pixel in the 60-frame period is 20 or more, the area is identified as the moving picture area 40. As illustrated in FIG. 6, the video area 40 is an area where the number of counts of each pixel is 20 or more and 60 or less (20 ≦ video area ≦ 60) during the 60 frame period.

The partition of the video region 40 can be known through the coordinate values of each pixel constituting the video region 40. In FIG. 6, the first left pixel among the pixels constituting the video region 40 is the pixel (min_row, min_col) having the smallest coordinate value of the row and column, and the end portion of the video region 40 in the row or column according to the first pixel. A pixel located at is a pixel having a maximum row coordinate value (max_row) or a maximum column coordinate value (max_col). From the coordinate value of this pixel, the division of the video area 40 can be known correctly. That is, the video area 40 can know exactly how long and the width is based on the coordinate value of the pixel.

When a video such as a real-time movie on the Internet is played back in the video region determined by the video detection unit 38 as the video region 40, the black region 50 is seen at the top and bottom. If the black region 50 is identified as the moving image region 40, the black region to be stopped flickers, thereby degrading the quality of image quality. To solve this problem, the video detecting unit 38 can solve the problem by accurately detecting the black region 50 in the video region 40 and distinguishing the black region 50 as the still image region. The detection of the black area 50 determines the area by ignoring the minute change in the gray level by dropping the resolution when searching for a video frame as shown in FIG. 8. That is, the video detecting unit 38 searches for 10 gray intervals when searching for a video frame and compares the luminance difference between pixels. In order to prevent an error in which there is a difference in data between pixels due to minute gray level differences, the edge search is used to determine the offset value of the video frame search so that a certain gray level difference (e.g., 20 gray differences) or less is determined by the same data. By increasing the size, the black region 50 is detected by discriminating the video edge region while ignoring the minute data difference. In addition, the black region 50 is determined by assuming that there is a margin between the border and the image when checking the discontinuity of the video frame and the image portion. The black region 50 may be a black color or a different color.

In the lookup table 39, values of gamma-compensated digital data according to input data Ri, Gi, and Bi are mapped to determine values of gamma-compensated digital data according to values of input data. The lookup table 39 supplies the timing controller 36 with the value of gamma-compensated digital data mapped to the input data Ri, Gi, Bi of the pixel average luminance of the still image area or the moving picture area for a certain frame period. Done. Here, the still image area shows the average luminance of a certain pixel that is almost no difference compared to the previous frame, whereas in the moving image area, the average luminance of the pixels is much different from the average luminance of the previous frame. In this way, the gamma curve having a constant gamma value corresponding to the average luminance of the pixels by the lookup table 39 is supplied to the still image region in the still image region determined by the moving image detector 38, and is provided by the moving image detector 38. The determined video region may change the gamma value of the lookup table 39 to supply the gamma curve, which is a stretch of the existing gamma curve, to the video region, thereby displaying the video more dynamically.

The gamma curve is a curve having a gamma value according to the input data. The X axis represents an input gradation and the Y axis represents an output gradation of a pixel. Depending on how you adjust the slope of the gamma curve (Output = Image ^{1 / Gamma} ), you can express natural continuity more clearly by changing the tones except for white and black. For example, in FIG. 9, when the video of the gamma curve is tilted to 1 and the video of the gamma curve to 1.3 is compared, the slope is increased, so that the gradients of the low gradation, the middle gradation, and the high gradation are combined. By increasing, the low gradation, middle gradation and high gradation parts are emphasized. In addition, the gamma curves shown in FIGS. 11 to 13 illustrate an embodiment in which the image quality of the video is changed as the inclination of each grayscale portion increases. That is, FIG. 11 is a graph and a video image in which the middle gray of the gamma curve is highlighted, FIG. 12 is a graph and a video in which the low and high gray of the gamma curve are highlighted, and FIG. 13 is a graph and a video in which the low and middle gray of the gamma curve is highlighted. Indicates. The video shown in FIGS. 11 to 13 can be seen that the darker the darker the lighter than the original image of the video shown in FIG.

The timing controller 36 supplies the digital video data R _O , G _O , B _O supplied by the lookup table 39 to the data driving circuit 35 and supplies the timing signals Vsync2, Hsync2, DCLK2, DE2. The control signal (GDC, DDC) for controlling the gate driving circuit 34 and the data driving circuit 35 is generated using. The data driving circuit 35 converts the digital video data R _O , G _O , B _O into an analog gamma compensation voltage and supplies the same to the liquid crystal display panel. A gate start is applied to the control signal GDC of the gate driving circuit 34. A gate start pulse (GSP), a gate shift clock (GSC), a gate output enable (GOE), and the like, and a source start is included in the control signal DDC of the data driving circuit 35. A pulse includes a source start pulse (SSP), a source shift clock (SSC), a source output signal (SOE), and a polarity signal (POL).

14 to 15 are flowcharts showing the control procedure of the video detecting unit 38 step by step.

Referring to FIG. 14, the video detecting unit 38 compares luminance values, which are data values of each pixel, during a previous frame period, and counts the number of conversions when determining a moving image area based on a difference in luminance values of each pixel through the comparison. . When the counted value is 20 or more, the area is determined as a moving picture area (S1).

After the step S1, the non-video area of the previous frame which is not detected by the video detector 38 undergoes a process of detecting the video area once again through the step of recognizing the video area shown in FIG. 15. (S2) The error can be reduced by repeating the detection of the moving picture area several times.

The moving image area detected after the step S2 is subjected to data stretching to supply a gamma voltage to the moving image area (S3).

As described above, the liquid crystal display device and the driving method thereof according to the present invention arrange a look-up table outside the moving picture detector and determine the exact moving picture area by the moving picture detector to perform data stretch gamma on a moving picture displayed on a screen such as a still picture. The present invention relates to improving display quality by supplying a curve.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (6)

A moving picture detection unit for determining moving picture data and still picture data by comparing luminance of input data and partitioning a moving picture area in which the moving picture data is to be displayed; A gamma correction unit for converting gamma characteristics of the moving image data to be displayed in the moving image region from those of the still image data; And And a display driving circuit which displays data on which the gamma characteristic is converted by the gamma correction unit on a liquid crystal display panel. The method of claim 1, And a background screen displaying the video area and the still image data is displayed together on one screen. The method of claim 1, The video detection unit, Detects the luminance of the input data during a plurality of frame periods and compares the luminance for each pixel unit, and converts the data whose pixel luminance values of the previous frame period and the next frame period are equal to or greater than a predetermined reference value during the plurality of frame periods into moving image data. Liquid crystal display device characterized in that judging. Determining moving image data and still image data by comparing luminance of input data; Partitioning a video region in which the video data is to be displayed; Converting a gamma characteristic of the moving image data to be displayed in the moving image region from a gamma characteristic of the still image data; And And displaying the data obtained by converting the gamma characteristic on a liquid crystal display panel. The method of claim 4, wherein And a background screen displaying the moving image area and the still image data is displayed together on one screen. The method of claim 4, wherein The determining of the video data and the still image data may include: Detecting the luminance of the input data for a plurality of frame periods and comparing the luminance for each pixel unit; And And determining, as moving image data, data whose pixel luminance values of a previous frame period and a next frame period are equal to or greater than a predetermined reference value during the plurality of frame periods.

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